Method of and means for loudspeaker sound wave distribution



Sept'. 3, 1968 o. E. KRAUT 3,400,217

METHOD OF AND MEANS FOR LOUDSPEAKER SOUND WAVE DISTRIBUTION Filed Feb. 8, 1965 FIG.2

FIG. 3

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United States Patent 3,400,217 METHOD OF AND MEANS FOR LOUDSPEAKER SOUND WAVE DISTRIBUTION Oscar E. Kraut, 455 Franklin D. Roosevelt Drive, New York, N.Y. 10002 Filed Feb. 8, 1965, Ser.'N0. 431,132 5 Claims. (Cl. 179-1) ABSTRACT OF THE DISCLOSURE Flush mounted, vertically oriented loudspeakers are front-loaded by cones of solid material which diffuse and reflect the sound in a 360 degree angle. The cones have an angle of taper sharper than that of their respective speakers, a sharp angle where the base meets the side, and are spaced from the supporting grill.

This invention relates to loudspeaker units, devices and assemblies, and an object of the invention is to provide a device which will reproduce all audible frequencies within the wide audible spectrum ranging between 30 and 20,000 c.p.s. with the most accurate fidelity possible at the present time.

With the advent of stereo reproduction from source material emanating from stereo records, tape, and FM multiplex broadcast, the problem of reproducing a real three-dimensional audio image through the widest listening area of any room or auditorium has become increasingly important. The aim of high fidelity audio reproduction has been to reproduce all audible frequencies as faithful to the original sound source as possible, with absolute exactness as the ultimate goal.

Up to the present the final transducer of the audio reproduction system has been some form of electromechanical mechanism designed to produce sound waves and project them directly at the listener. This has been especially important in the reproduction of the higher frequencies, since their increasingly shorter wave length at increasing frequencies makes them increasingly fragile and more difficult to project any appreciable distance and yet remain as audible as the lower frequencies. In some large auditoria, such as moving picture houses and concert halls, this problem has been serious enough to use special horns for projecting frequencies from about 500 c.p.s. upward. In general, the more successful the transducer is in producing high frequencies the more directional it is, especially when the device is a dynamic loudspeaker. An angle of dispersion of as much as 90 degrees is the exception in speakers producing high frequencies, with most falling into narrower beams of sound.

With the advent of stereo sound reproduction this narrow beam of sound has resulted in limiting the area in which a stereo image, soundwise, can be heard, since this occurs only in the area where the speakers used overlap in their output, that is, where their widening conical beams of sound meet and intermingle with each other. Thus it is apparent that the beaming of a concentrated pattern of sound also results in being able to hear the produced audible spectrum in full in a limited concentrated area, even monophonically. Each such sound beam is analogous to a light projector producting a hot spot of light.

It becomes clear that in order to produce a stereo sound result with most effective coverage in listening area, the transducers in the device must have the widest area of dispersion. Further, it has been proved that the human car derives its most acute clue to the location of a sound source from the upper frequencies above 500 c.p.s. where the difference in phase on the two sides of the head is greatest. The reverberation time of the room in which the sound is being produced is also an important factor in determining the direction of the sound source. In most investigations and tests, the frequencies below 500 c.p.s. are relatively non-directional, and while they are easily produced, projected over wide areas and easily heard, they offer human ears the least information in determining the direction of the source relative to the listeners position.

There are additional considerations involved in reproducing sound source material accurately in three dimentional aspect to the listener. For example, stereo recording of the original sound source employs two or more microphones which are, in effect, point sound auditors or registers like the human ear, and which record all sound data accumulating at the positions they occupy in the room. This sound record, whether recorded on tape, phonograph record, or directly broadcast, is then reproduced by the high fidelity stereo receiver and finally directed at the listener by direct radiating loud speakers which are again, in effect, point sources of sound produced more or less unilaterally.

The important consideration up to the present state of the art has been the accurate reproduction of all audible frequencies with as close to the exact intensities and inherent distortions, or lack of them, as possible. However, little source material is actually produced directly at the listener, especially where music is concerned, since most musical instruments produce their sound upward, downward or sideward, for example, violins, oboes, clarinets, flutes, pianos, etc. Reverberation and reflection, therefore, play a very important role in the production of live sound in any room or auditorium.

With the above considerations in mind, I have developed a speaker means, device or system wherein the emphasis is not only on the accurate reproduction of all frequencies contained in the original source with little or no additional distortion, as heretofore, but also in placing great emphasis on a method and means of dispersing the sound in order to produce more accurate and lifelike effect in greater accordance with the original to offer the listener audible information in a manner similar to the original.

In the area of 30-500 c.p.s. 'I employ a driver designed to accurately produce this range in an infinite baffle designed to realize the lowest frequencies of the range as well as all those above the lowest, with this driver facing forward toward the listener. Since this area of frequencies is relatively non-directional, whatever vestiges of directional information it does contain should be left as undisturbed as possible. To clarify this aspect briefly, the lowest frequencies will contribute to gross indications that sound or music is emanating from an area in front of the listener and not to the side of, or behind or around the listener, that is, the orchestra playing is on stage and not surrounding the listener sitting in the auditorium. There are two aspects to the non-directional aspects of the base or low frequencies. First, the wave lengths are so large that they are easily guided by walls and flow around objects normally positioned between the listener and the source, so that such frequencies can be heard clearly almost everywhere; and second, such frequencies are not critical or helpful in pinpointing the exact spot that the sound is coming from to the listener.

Where the frequencies begin to become increasingly important in establishing point source of sound origin for the listener I have devised a new dispersion means or system for radiating midand high-frequencies in a manner. more analogous to the originally produced sound waves. I have taken specialized loudspeakers of quality design (dynamic loudspeakers) and have caused their output to be reflected, diffracted and diffused so that the emanating sound waves are not only directed at the listener but also in a full 360 degree radiating pattern laterally, horizontally and, to a lesser degree, vertically upward. The object here is to expand the point source of the loudspeakers which are now reversing the process done by the microphones picking up the original. The loudspeakers energized by electrical signals originally produced by the microphones from sound waves converging on their respective point positions, are now translating the signals into sound waves. I am now carrying this process one step further and am directing sound in a complete radial pattern so that the area behind and around the sound source (the loudspeaker) is contributing toward placing individual instruments more exactly in relative position in the listening room not only in a lateral plane from left to right but also from front to back, with the speakers appearing to delineate the front of the performing area.

It is, of course, impossible at the present state of the art to exactly recreate the original acoustic conditions and accurately reproduce the various sound waves, direct and indirect which converged on the original microphone positions, especially where the listening room differs from the room in which the sound was originally produced. However, through the use of the dispersion means and system which I have devised, this goal can be approximated relatively to a degree unrealized heretofore.

A mid-range and a high-frequency speaker, both chosen for their most effective performing qualities and accuracy of result frequency-wise, are mounted flush in the top of the woofer housing, that is, flush with the top surface thereof, in an approximately diagonal pattern to minimize phase differences from any position in the 360 degree pattern around them so that one does not sound behind the other from any angle of normal listening. These two speakers thus face upward relative to the woofer.

An inert cone of predetermined size and angle, fabricated from some solid, inert hard material such as, for example, hard wood or plastic, is suspended above each of the speakers which face upward, that is, those which radiate frequencies above 500 c.p.s.

It should be added at this point that all the drivers used should be restricted to specialized areas of sound for which they are best suited and chosen, through the medium of an electrical dividing network designed to effect a slow transition from the range of one driver to another, preferably at the rate of six to twelve decibels per octave at the crossover points. This also minimizes whatever phase differences exist between the front radiating woofer and the upwardly radiating midand high-frequency drivers.

In order to concentrate the energy produced :by the upwardly-radiating drivers, the cone suspended over each must be brought down coaxially with and as close to the speaker as possible without interfering with the speakers free action under even maximum power. This, in effect, loads the upward radiation of the speaker. Midand highrange sound waves now produced by the speakers will now be striking the cones in such manner that frequencies, depending on their wave lengths, will be diffracted and reflected in a lateral and radial pattern of 360 degrees in the horizontal plane. The vertical dispersion angle will correspond to the angle formed between the inert cone and the radiating cone of the speaker. In order to extend this vertical angle of dispersion as much as possible, since the lateral is already at maximum, the inert cones are fashioned to have a sharp edge around their now upturned ibases. It is known that there is an abnormal concentration of energy to be found at such edges. In order to utilize this concentration and diffract it around the lip orperimeter of the base of the cone, the cones are suspended from a supporting structure by means of a screw with a spacer or gasket interposed so that the circumferential edge of each cone is left free. This, in effect, tends to reduce the sound shadow created by the cone along the axis of the speaker, or directly upward. However, since the area within the sound shadow of the cone is the area of least effectiveness sound-wise, the instant dispersion system is independent of variations in ceiling height, which otherwise could greatly alter performance.

To minimize shadow effect in the area of maximum effectiveness sound-wise, namely the 360 degrees laterally as well as in the angle described above relative to vertical dispersion, and also to further diffuse the combined output of the midand high-frequency drivers, the structure supporting the inert cones and their spacers or gaskets, is fabricated totally out of a material with a fine perforation pattern. The material used must be of such a character that a thin sheet of it can be fashioned to provide the necessary strength and protection both to support the cones fairly rigidly and precisely over the drivers and to withstand the rigors of shipment; an example of such material is ZO-gauge aluminum. The advantage of a thin material is the avoidance of the creation of perforations which because of their axial length become a series of minute tubes rather than just holes. A pattern chosen from among those available commercially has a thirty-seven percent open area with each hole acting as an individual diffusing lens; this pattern was the most open offered commercially. Theoretically, this aspect of greater percentage of open area, if feasible and available, should improve the net result of sound quality.

The quality of sound produced by the instant instrument has been universally found to be more natural and lifelike than produced by the best instruments heretofore available and the dispersion effect has been startling and overwhelming. The instrument performs normally under widely divergent accoustic conditions and gives an evenness of dispersion such that an expert listener finds the sound and the stereo effect following him almost everywhere in the store or the listening room.

What is absent from the prior art but which is provided by the present invention is that the direct radiation of the woofer has been coupled with total 360 degree radiation, reflected or otherwise, of the remainder of the audible frequency area, that is, above 500 c.p.s. There is nothing new in placing a woofer in an infinite baffle, per se, but the dispersion system or means described above as devised and assembled is novel over the prior art. Upward radiation has been used, generally with the woofer also' directed upward or positioned at the opposite end of a tube radiating downward toward the floor. Attempts have been made to use reflection but without front loading of the speaker, with the consequence that the reflection, if any, has been weak and inadequate and hence muffled in sound and grossly unbalanced so that the bass predominates. The instant dispersion system of loading the speak-.

ers with resultant reflecting and diffracting the waves of each speaker according to its character and audio area; the employment of the edges of the cones introduced coaxially over the speaker, and, further, the suspension of the cone floating, as it were, in an area totally open and with no appreciable obstruction to cast sound shadows and heighten the distortion of the emanating sound, are all novel features of the present invention.

The foregoing discussion sets forth descriptively the broad objects and novel features of the present invention. The accompanying drawings illustrate an embodiment of the invention.

Referring briefly to the drawings, FIG. 1 is a front elevational view of a loudspeaker device embodying features of the invention.

FIG. 2 is a side elevational view of the same, with parts broken away and partly in section.

FIG. 3 is a top plan view, with parts broken away and partly in section, and with the perforated cover removed.

FIG. 4 is a top plan view of the device with the cover in place.

FIG. 5 is a sectional view taken on the line 5-5 of FIG. 4.

FIG. 6 is a sectional view taken on the line 66 of FIG. 1.

FIG. 7 is a fragmentary rear elevation-a1 view of the device.

FIG. 8 is a sectional view taken on the line 8-8 of FIG. 6. I

FIG. 9 is a wiring diagram of the device, showing a set of constants which have provided a suitable crossover network.

Referring in detail to the drawings, the numeral 10 indicates an upright housing or cabinet having opposed side walls 11 and 12, a rear wall 13, and a front wall 15 which extends part way upward from the base of the cabinet, thus leaving the greater portion of the front of the cabinet open. This opening 14 is closed by a screen or mesh 16, preferably of metal, contained within a frame 17. This frame is removably secured against the front edges of side walls 11 and 12 by frictional registration of pegs 18 in recesses 19 in the said edges, FIG. 3. A second front wall 20 is mounted behind the wall 15 and the opening 14 in any suitable manner, not shown, and has an opening in which a woofer 21 is mounted in the usual manner. The carpentry of the cabinet as so far described is of no particular significance.

The top wall of the cabinet is indicated at 22. Preferably along a diagonal, that is, along the line 5-5 of FIG. 4, two spaced circular openings 23 and 24 are provided with their axes on the said line. The opening 23 has a smaller diameter than the opening 24 and therein a tweeter 25 is mounted to discharge its sound wave output in a generally upward direction, and with its circumferential edge 26a positioned flush with the upper surface of the top wall 22. In the opening 24 a mid-range speaker 26 is similarly mounted. The centerpoints of these two speakers are shown at 27, FIG. 5, in the form of teats or buttons.

The tweeter and mid-range speakers preferably used in the instant device have no back radiation, as their metal baskets, not shown, are solid behind their radiating cones; these speakers are available on the market. However, other speakers in the desired frequency areas could be used, and they are more conventional since they are designed to radiate backward as well as forward. In case the latter type of speakers were used, the cabinet would be partitioned or divided internally so that each of the three speakers of the device would have its own bafile area completely separated from the other two, all not shown.

A thin, preferably metallic perforated cover 28 is provided, having a roof portion 29, side wall portions 30, and inturned flange portions 31. The top wall 22 of the cabinet has peripherally spaced pegs 32 protruding upward therefrom, and the flange portions 31 of the cover have preferably rubber grommets 32 therein complementary to the pegs, to secure the cover on the said top wall 22.

Suspended from the roof 29 by screws 33 and 34, and separated from contact with the roof by rubber or the like spacers 35, are solid cones 36 and 37 made of wood or plastic. The cone 36 is substantially in axial alignment with the tweeter 25 and the cone 37 is likewise in alignment with the speaker 26. The apices of these cones are spaced above the centerpoints of the respective speakers a distance just sufiicient to prevent mutual contact between these parts at maximum amplitude of the speaker. It is to be noted that the solid cones have slightly sharper angles than their respective cone speakers, and also that the bases of the inverted solid cones are shown having the same diameters as the diameters of the speaker cones. These relative dimensions appear to give best results, and may be expressed, as

a rule of thumb, that the diameter of the base of the solid cone should be no larger than the diameter of the driver. This is a compromise between too large and wide and too small and narrow a solid cone. The solid cone must be large enough to offer optimum surface for reflection, deflection, or diffraction, and it must be small enough to allow a decent vertical angle of dispersion to enable a person standing relatively close to the speaker to hear everything emanating therefrom, as well as persons sitting or standing distant therefrom in a listening room. It is also obvious that there is little or no reflection of sound waves back from. the cones to the speakers.

The spacers 35 are sufficiently smaller in diameter than the bases of the cones to leave the sharp peripheral edges of the cones free to vibrate, as discussed above. Rubber pads or the like 38 are secured to the flanges 31 of the cover 28. Both these provisions serve to dampen or prevent unwanted vibrations in the cover.

FIG. 9 shows the cross-over network, or wiring diagrarn, of the device. The output of an amplifier, not shown, is connected to the terminals 39. A potentiometer 40 is shown for the tweeter and a second potentiometer 41 is shown for the mid-range speaker. Thus the two speakers can be adjusted to achieve the smoothest possible reproduction to suit the individual taste. Otherwise it is believed unnecessary to discuss the wiring diagram in detail.

The sound waves which emanate generally upward from the speakers 25 and 26 are diffracted and reflected by the solid cones suspended above them, throughout a 360 degree wide horizontal angle and through a large vertical angle, as previously discussed. The small perforations in the thin metal, plastic, or the like cover screen 28 offer additional aid in dispersion of the emanating sound waves of both drivers.

-I claim:

1. A loudspeaker system comprising in combination, a cabinet,

first speaker means mounted in said cabinet to radiate sound waves below approximately 500 c.p.s. in a generally horizontal direction,

second speaker means mounted in said cabinet to radiate sound waves above approximately 500 c.p.s. in a generally upward direction,

said second speaker means further comprising means for diffusing, dilfracting, and reflecting said second mentioned sound waves in a 360 degree wide horizontal angle,

said last-named means comprising (1) a midrange speaker for radiating sound waves of the frequency range from approximately 500 c.p.s. to 3500 c.p.s.,

(2) a high range speaker for radiating sound waves of the frequency range above approximately 3500 c.p.s.,

(3) said midrange and high range speakers flush mounted with the top of the cabinet to enfiance horizontal dispersion of the sound radiating therefrom,

(4) an inverted cone of solid material suspended above each of said 'midrange and high range speakers and as close to said speakers as voice coil movement permits thereby front-loading said speakers,

(5) each of said cones having a base which forms a sharp angle with its side, said base being no larger than the cone area of its respective associated speaker,

(6) said cones suspended by an acoustically transparent perforated screen rigidly attached to said cabinet.

2. A loudspeaker system according to claim 1, said cabinet having a substantially rectangular horizontal cross-section, the axes of said cones and of their res positioned substantially in diagonal of said horizontal spective associated speaker a vertical plane through a a cross-section. 3. A loudspeaker system according to claim 2,' said first speaker means mounted in the front wall of said cabinet, said high range speaker being positioned closerv to said front wall than said midrange speaker.

4. A loudspeaker system according to claim 1, the angle of taper of each of said cones 'being smaller than the angle of taper of the conical diaphragm, of its associated speaker.

5. A loudspeaker system according to claim 4, said cones having spacer members of smaller diameter than the bases of the cones positioned between said screen and the cones.

FOREIGN PATE S 10 1957 England. ,l f

KATHLEEN H. CLAEFY, Primary Eqca mil ler 1 R. P. TAYLOR, Assistant Examiner. 

